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Lepticidium
Lepticidium (meaning "graceful weasel" in Latin) is an extinct genus of small mammals; together with macropods, giant pangolins, and humans, they are the only known completely bipedal mammals.[citation needed][dubious – discuss] Comprising eight species, they resembled today's elephant shrews. They are especially interesting for their combination of characteristics typical of primitive eutherians with highly specialized adaptations, such as powerful hind legs and a long tail which aided in locomotion. They were omnivorous, their diet a combination of insects, lizards and small mammals. One of the first branches to split from basal eutherians,1 they appeared in the Lower Eocene, a time of warm temperatures and high humidity, roughly fifty million years ago. Although they were widespread throughout Europe, they became extinct around thirty-five million years ago with no descendants,2 probably because they were adapted to live in forest ecosystems and were unable to adapt to the open plains of the Oligocene. Leptictidium is a special animal because of the way its anatomy combines quite primitive elements with elements which prove a high degree of specialization. It had small fore legs and large hind legs, especially at the distal side (that further from the body). The lateral phalanges of its forelegs (fingers I and V) were very short and weak, finger III was longer and fingers II and IV were roughly equal in size, and slightly shorter than finger III. The tips of the phalanges were elongated and tapered.1 Leptictidium is a special animal because of the way its anatomy combines quite primitive elements with elements which prove a high degree of specialization. It had small fore legs and large hind legs, especially at the distal side (that further from the body). The lateral of its forelegs (fingers I and V) were very short and weak, finger III was longer and fingers II and IV were roughly equal in size, and slightly shorter than finger III. The tips of the phalanges were elongated and tapered. Artist's impression of a Leptictidium The and the were quite loosely fixed, while the had a flexible joint with only one vertebra. The anteorbital in their crania suggest they probably had a long and mobile snout, similar to that of elephant shrews. Leptictidium had wide in the antemolar row, its upper were more transverse than those of the North American and its fourth were molariform. Its C1 were incisiviform. Its was quite small in comparison to the size of the and the animal as a whole. It varied between 60 and 90 cm (24–36 in) in length (more than half of which belonged to the bald tail), and 20 cm (8 in) in height. It weighed a couple of kilograms. These sizes could . Locomotion[] L. nasutum fossil One of the mysteries about Leptictidium is whether it moved by running or by jumping. Because there are very few completely mammals, it is difficult to find an appropriate living model to compare it with. If the is used, it is probable that Leptictidium hopped along with its body tilted forward, using its tail as a counterweight. On the other hand, combine both types of ; they usually move , but they can run on two legs to flee from a predator. Studies of the bone structure of Leptictidium have yielded contradicting information: its leg appear too weak to have supported the shock of repeated jumps, but its long feet were obviously adapted for jumping rather than running. Kenneth D. Rose compared the species L. nasutum with the . L. dakotensis had a series of traits which show it was a running animal which sometimes moved by jumping. Despite the marked similarities between Leptictis and Leptictidium, there are certain differences in their skeletons which prevent the example of Leptictis from being used to determine with certainty the way Leptictidium moved: the most important being that, unlike Leptictis, the and the of Leptictidium were not fused together. Behaviour[] Perfectly preserved of three different species of Leptictidium have been found in the in . The marks on their fur have been preserved, as well as their contents, which reveal Leptictidium were which fed on , and small . The of L. tobieni also had pieces of and notable amounts of sand in its abdomen, but it cannot be determined with certainty if the animal swallowed it. Since Leptictidium young were very vulnerable to attacks of predators, it is probable that they were born quite developed and that they became independent when they were still quite young. From the behavior of today's elephant shrew, the possibility can be suggested that Leptictidium young went out to hunt with their mother, and that they learned to distinguish prey by licking their mother's mouth when she had just caught an animal, in order to know the flavor of food. However, the presence of bones suggests that, like and (as well as most other non-placental mammals), they instead gave birth to larval young. Habitat[] Main articles: and Leptictidium and as shown in Walking With Beasts on in , Leptictidium lived in the of the . From the beginning of this period, the temperature of the planet rose in one of the quickest (in terms) and most extreme episodes of global warming in the geological record, termed . It was an episode of quick and intense (of up to 7 °C in high latitudes) warming which lasted less than 100,000 years. The thermal maximum caused a great extinction which is used to distinguish the Eocene from that of the . The global climate of the Eocene was probably the most homogeneous of the ; the from the to the was half that of today's, and the deep were exceptionally warm. The polar regions were much warmer than today, possibly as warm as the present-day of North America. Temperate forests reached the poles themselves, while rainy tropical climates reached 45° N. The greatest difference was in temperate latitudes; nevertheless, the climate at the was probably similar to today's. In the Eocene, most of what is now , the and south-west was submerged under the . These two were separated by the (an ). Due to high humidity and temperatures, most of the European continent was covered in . , , a saturated with reactive gases similar to the one once found in the Messel pit zone. The region which today is was in a active zone during the Eocene. It is thought that the could have been the old location of a volcanic lake saturated with . The lake would periodically release the gas it contained, creating a lethal cloud which would asphyxiate any animal in its path. This would explain the great number of non-aquatic species which have been found in the old lake-bed of the Messel pit. In the lush forests of this region, Leptictidium shared its habitat with animals such as , , or . There were also predators, the crocodilian , the , and the . Species[] The genus Leptictidium includes eight . These include: Leptictidium auderiense[] L. auderiense Described by in 1962 based on a series of from the faunal stage. Tobien also uncovered a small skeleton he defined as a of the species, but Storch and Lister proved in 1985 that, in fact, the skeleton did not even belong to the Leptictidium. It was the smallest species of all and was only sixty centimetres long. Several skeletons have been found at the Messel pit. Mathis remarks the exceptional development of the paraconid (or mesiobucal cusp) of the lower P4 . Its premolars and were quite small in comparison to the dentition as a whole. The name of the species refers to the settlement of . Leptictidium ginsburgi[] Described by Christian Mathis in 1989. Fossils have been found in the lagerstätte at Robiac, Le Bretou, Lavergne, La Bouffie, Les Clapiès, Malpérié and Perrière (), in strata. The mesostyle typical of the Leptictidium genus is not developed in this species. The species is dedicated to , and deputy director of the in . Leptictidium nasutum[] L. nasutum Described by and in 1985. It was a middle-sized species which was seventy-five centimeters long. Several skeletons have been found in the Messel pit, in strata. The tail of this species had 42-43 , a number surpassed among solely by the . Its and teeth were quite small in comparison to the dentition as a whole. The name of the species refers to the of the animal. The is the complete skeleton of an adult specimen kept in the in . Leptictidium sigei[] Described by Christian Mathis in 1989. Fossils have been found in the lagerstätte at Sainte-Néboule, Baby, Sindou and Pécarel (), and it has a more primitive appearance than L. nasutum. It is known mainly from isolated teeth. It has a P4 with a much reduced paraconid, as well as very distinct entoconids and hypoconulids on M1 and M2. The species is dedicated to , . Leptictidium tobieni[] Fossil of L. tobieni at the . Described by and in 1987. It was the largest species of all at ninety centimetres long. It is one of the species found in the Messel pit, in strata. The species is dedicated to , descriptor of the genus Leptictidium and promotor of research in the Messel pit during the 1960s. The is a complete and perfectly preserved skeleton of an adult specimen which was uncovered in September 1984 and which can be found at the Hessisches Landesmuseum Darmstadt. There is also a paratype; a non-complete and badly preserved specimen which can be found at the Institut Royal des Sciences Naturelles de Belgique. It has a relatively robust with a relatively large mesostyle. The molariform premolar teeth are a characteristic of the Leptictidium genus as a whole which is very marked in the P4 premolars of L. tobieni. The well-developed mesostyle and the transversal configuration of the upper molars are other typical traits of this species. Comparison of the Messel species[] By observing the clear morphological differences in the dentition of the three species found in Messel, the possibility can be discarded that either the discovered are specimens of the same species but of different age, or that two of these forms belonged to the same species with a marked . The Messel species developed very quickly a series of characteristic evolutionary traits, common to all of them, which separate them from the lagerstätte of . This table compares the size of different specimens of each species found in the Messel pit . Category:Ice Age Beasts